1. Field of the Invention
This invention relates to magnetic signal transducers, also known as heads in the art, such as may be used in storing information in a magnetic storage medium, like magnetic tape, and in retrieving the information stored therein and, more particularly, this invention relates to an assembly for holding and supporting and varying the position of magnetic signal transducers.
2. Description of Related Art
As is known in the magnetic tape transport art, helical-scan magnetic tape transports employ one or more mounting assemblies for supporting and adjustably positioning a magnetic transducing head in a rotating drum. One such assembly is disclosed in U.S. Pat. No. 4,212,043, which was filed Nov. 1, 1978 and which issued Jul. 8, 1980 and which is incorporated herein by reference. There, adjustable mounts are secured to the interior of the rotating drum and extend radially toward the periphery of the drum with the head protruding through an opening in the drum to scan the recorded tracks on a magnetic tape curved around the periphery of the drum in a helical path. This adjustable mount permits the head to move laterally with respect to the length direction of a recorded track. Each adjustable mount, also known as a flexural pantographic mechanism in the art, includes a pair of parallel bending or pivoting leaf members anchored at one set of ends to a fixed body. The leaf members extend as cantilevered beams with the transducing head assembly mounted near the opposite set of ends in a manner so that the head assembly can operate as a moveable body. Each leaf assembly is suitably constructed so that, when a control voltage is applied such as by a tape transport head positioning servo system to a voice coil assembly, the leaf members deflect accordingly, thereby displacing the transducing head supported thereon. The extent and direction of the deflection of the head is proportional to and a function of the amplitude and polarity of the control voltage applied to the voice coil. When used in combination with a servo system feedback circuit, the head may be positioned in an optimum location for following a tape track, which has been recorded on the magnetic tape medium.
Such a head positioning arrangement has some disadvantages. For example, the inherent flexibility of usually long, thin head positioning leaf members sets up undesirable resonances in the leaf members under rapid and repetitive flexure loadings. Such resonances also result in undesirable deflections under repeated flexures of the leaf members. The occurrence of such conditions in the leaf members under the desired loading sequence can severely impair the ability of a head mounted on a leaf member to accurately follow a magnetic tape track. Such undesirable conditions can be substantially aggravated unless the frequencies of higher mode vibrations, also called oscillations in the art, are raised substantially higher than the frequency bandwidth of a suitable closed loop servo system of which the mounting assembly is a part.
The primary, or first, mode stiffness K of a leaf member is defined as the ratio F/D, where F is a component of a force that is perpendicular to the plane of a leaf member and D is the deflection of the leaf member. Since the power utilized in producing the force, and hence the deflection, increases with increasing primary mode stiffness, it is desirable to design the leaves in such a manner so as to minimize the primary mode stiffness. At the same time, it is desirable to raise the frequencies of the vibrations of the higher order modes so as to attenuate the undesirable excitation from the higher frequency oscillations mentioned above. The higher order mode frequencies can be raised by increasing the higher order mode stiffness of the leaf members to values beyond the designed bandwidth of the closed loop servo system, i.e., the higher mode frequencies can be increased so that any undesirable excitation that they may put upon the servo system is so significantly attenuated that the servo system, for all practical purposes, is not subjected to those undesirable effects of the higher order mode vibrations.
It has been found that the dual requirements of suitably low primary mode stiffness and suitably increased higher order mode stiffness cannot be economically met using leaves of uniform thickness and width. U.S. Pat. No. 4,212,043 discloses a solution to this problem wherein the leaf thickness is not uniform. Instead, stiffening members are attached to the central portion of both sides of a much thinner leaf to form laminated leaf composites. This solution, however, can be costly since more parts and additional assembly steps are usually required. Moreover, the stresses on the end portions of the leaves which do not contact the stiffening members are so highly concentrated that it often necessitates that a costly, very thin, high yield strength material be used for this composite laminate construction to maintain the same low primary mode stiffness as with an equivalent constant leaf thickness pantograph mechanism.
Thus, what is desired is a simple and cost effective solution which satisfies the dual requirements of lower primary mode stiffness and increased higher order mode stiffness.